Your timing is everything
Finding the right time to hit the loo on a plane is an art form, right up there with painting and good Botox. Go too early, and you’ll risk the whole plane knowing it was you who stunk up the joint. Go too late and, well, it’s a pretty uncomfortable flight.
The best time to poop on a plane is right after the flight attendants bust out the beverage cart. Most people won’t get up and risk getting stuck behind it, so you won’t fight lines, and it’s unlikely that you’ll find anyone waiting when you get out.
If you miss that opportunity, go when there’s a small (keyword: small) line for the lav. There will be an inherent diffusion of defecation, whereas it’ll be hard to pin down who, exactly, was the pooper.
Pick the right lavatory
On a lot of planes you won’t really have a choice, so the “right” lavatory is the one with an operative bowl and a sink. But if you find yourself on a larger plane with entire bathroom sections, find the largest concentration of bathrooms and go there. Even if a line forms, they won’t all be waiting on you, so you can relax while you do your business.
Pack some baby wipes
Airplane toilet paper seems like it’s the result of a physics experiment to find the thinnest possible solid on the planet. You’ll use more of it to get yourself clean than you’ll need draft beer to catch a buzz in Utah, so pack a set of baby wipes in your carry-on. They flush down the toilet just fine and prevent both chafing and insufficient personal cleaning.